1. Field of the Invention
The present invention relates to an apparatus to detect the remaining amount of developer in a developing unit. More particularly, the present invention relates to an apparatus to detect developer level using an optical sensor.
2. Description of the Related Art
Generally, in an electrophotographic image forming apparatus, such as a laser beam printer, a developing unit develops an electrostatic latent image formed on a surface of a photosensitive medium with developer. The developed image is then transferred onto a paper sheet. That is, the developer supplied from the developing unit is stuck on the electrostatic latent image of the photosensitive medium and developed into a visible image, and the image is transferred onto the paper sheet. Thus, a printing operation is performed. To continuously perform such a printing operation, the developer must be continuously supplemented in the developing unit.
To supplement the developer, a unit to detect the remaining amount of developer in the developing unit has been commonly used. Conventionally, an optical sensor, installed on a bottom surface of the developing unit, generates an exhaustion signal indicating that the developer is almost exhausted. The optical sensor has a light emitting element and a light receiving element placed opposite to the light emitting element. When developer exists between the light emitting element and the light receiving element, the exhaustion signal is not generated. When the developer is almost exhausted and no developer exists between the light emitting element and the light receiving element, light is transmitted from the light emitting element to the light receiving element and the exhaustion signal is generated.
However, in the conventional method, the exhaustion signal is generated and a process of supplementing developer is performed only when the developer is almost exhausted. Thus, due to developer shortage, an image being printed on a piece of paper may be of low quality. Additionally, due to static electricity, the developer might be stuck on a light emitting surface of the light emitting element and a light receiving surface of the light receiving element. Thus, even when the developer is almost exhausted, due to the stuck developer, there is a high probability to wrongly determine that there is enough developer. Accordingly, because the developer is not supplemented at an appropriate time, low quality images may be printed.
To address this problem, a detecting apparatus that timely, precisely, and stably detects the developer level is needed.